Yes you can. I don't know what the pitch and diameter of the existing thread is but you may be able to find something that fits. Better yet, someone on this board may have a proper piece to offer. (Ask in a separate thread with the picture of your dizzy.)

The tubing you use should be a small diameter; otherwise the volume of air inside the length of tube may result in a bit of delay in reaction to changes in vacuum. An auto parts supply store may have something. It also has to be reasonably stiff-walled so it doesn't collapse.

One alternative is to find a tube that just fits inside the hole in the threaded part, insert it into the opening and seal with silicone sealant or equivalent.

Hey Dan can I just hook it up to a hose?  I was thinking a big enough house to fit over those threads on that vacuum unit , then maybe reducer to a smaller hose to connect the vacuum at the carb end??  

That is a much older type of distributor, probably from a MK1 car. It would have had a metal tube running from the dizzy across the front of the engine to above the thermostat. On one of the T'stat bolts would be a bracket holding vertically a metal moisture or vapour trap. From the top of the trap, the thin metal tube would continue along the back or top of the rocker cover to the carb, where it would be connected to the carb with a short piece of rubber tubing.

Your dizzy has another useful feature - the small adjustment knob at the bottom of the vacuum advance unit. This was used to fine-tune the spark advance to suit changes in operating conditions, such as altitude or differing fuels.

The original question was about rough idle on a HIF44. We are discussing mixture to improve idle. The screw referred to is the "jet adjusting screw" (Burlen), not the "throttle adjusting screw" (Burlen), if you need exact terminology.

No such thing as idle mixture on an SU.

Weber carbs yes, SUs no.

You may be thinking about idle speed adjustment screw which acts directly on the throttle linkage to open/close it minutely at idle.

The jet adjusts the mixture across the entire rev-range from idle to WOT

https://photos.app.goo.gl/HpwpMXMmrJjtS6YJ6

Hi guys on another note, the reason why I never had the vacuum connected was due to my dizzy vacuum unit has a threaded end.  It doesn’t look like your conventional unit where there is a nipple that would take a hose.  Any suggestions..   I will try to get a pic shortly 

Hi Dan, Actually I don't think it has much to do with the idle.  Most units need a reasonable level of vacuum before they start doing much.... and the engine doesn't use much fuel then anyway.  

Where you do save is at part throttle cruise...especially at a steady 60-70 mph on the open road..

Cheers, Ian

Thanks fellas for the insight.  I’m going to leave vacuum as is and cap that vacuum and adjust accordingly.  I’m not too concerned about fuel economy ??

Yes, the vacuum advance distributor is an economy device - when at idle, the vacuum advances the spark allowing for a leaner idle mixture, However, as you open the throttle, the vacuum to the distributor decreases and so does the advance. With the throttle open there is no vacuum advance but the mechanical advance takes over as rpms increase. 

If your distributor has a vacuum advance, you should have it connected. Thanks Ian.

Actually you need to (re?) install the vac advance on your distributor.  I found a 30% eduction in fuel usage when I fitted mine.

Cheers, Ian

Dan!  Your the man!  I’ll go ahead and cap
that off and try to adjust it as you stated and see how I do.....

An unused vacuum port should be capped. A short piece of hose/tubing with a small bolt will do.
When you cap it the idle is rough because it is now richer at idle than it should be. Adjust the idle mixture with the jet adjusting screw, remembering that on a HIF you turn it out for leaner or in for richer... counter-intuitive but is it because it works on a lever inside.

Your jet needle will be fine. Adjusting the mixture at idle will not affect significantly your state of tune at higher rpms because the volume of air and fuel coming in an open throttle is vastly more than what leaks through the vacuum port at idle. When you adjust the mixture, the lever moves the long jet up (leaner) of down (richer) slightly, maybe a millimetre or two. This exposes a little less (leaner) or more (richer) of the long needle, but only on the portion intended for idle. When you open the throttle, the dashpot piston is lifted up, pulling the needle farther out offering more fuel for the increased air flow. The needle and jet are now using the section of the needle intended for the higher rate of air flow with the throttle more open.

Adjust the mixture at idle no more than 1/4 turn at a time - the and take it for a test drive. The longer you sit there with the engine running and the car not moving, the warmer the HIF carb gets. The lever I mentioned has a bi-metallic component that leans the engine out as it warms up. This is to have a slightly richer idle mixture at cold start-up. The trouble begins when the engine is hot and not moving and the carb gets hotter than normal, the bimetal lever leans the mixture out as you try to adjust it... a vicious circle.

Ideally, your engine should have a smooth idle when at normal running temperature but would need a bit of choke to compensate until it warms up to running temperature - that's why they still have a manual choke (which is actually a "mixture control cable").

[edited to correct terminology]

Hi guys i have a hif44 that the vacuum advance unit is not hooked up to it.  For the longest time the mini has been like this, engine runs good and i have never seen my plugs lean.  My question is do i need to have this unit blocked off?  I have tried before and when i do block/cap it off the car idles rough like it wants to die.  Do i need to rejet to compensate for the the rough idle?  I think if blocking it off would result in a rich mixture correct?  Thanks in advance to all that respond.  





FAB